Appending a Grease Pencil rig breaks it
The rig you uploaded has been drawn on frame 3, while if you append it on a new scene it's set on frame one. Even if you go to frame 1 in the rig file some strokes disappear.
To solve, you can open a grease pencil dope sheet editor and grab all strokes to frame one, or simply start animating from frame 3 and above.